In the cigarette making machines, a continuous trimmed rod of cut tobacco is formed on a pneumatic suction belt and is then associated with a paper wrapping web to form a continuous cigarette rod, to be severed finally into individual cigarette lengths.
The cut tobacco for said rod is fed by the feeding hopper of the distributor, and the tobacco trimmed away from the rod, i.e. the trimmed excess tobacco, is recirculated to said hopper, and more particularly to a pre-hopper. Therefore, in the cigarette making machines, the distributor will not feed the cut tobacco in the strict amount which is necessary to for the tobacco rod, but in an excessive amount so as to permit the trimming away of the outside irregularities of the rod and thus to effect an exact sizing thereof. The amount of trimmed excess tobacco depends on the excess of the total flowrate fed from the distributor. By "total flowrate" is meant the sum of the rate of flow of cut tobacco actually used to form the rod and of the rate of flow of the recirculated trimmed excess tobacco.
The percentage of the recirculated trimmed excess tobacco is the ratio between the weight of the trimmed tobacco and the sum of the weights of both the trimmed tobacco and the tobacco issued as a rod. Practically, therefore, in order to determine this percentage, the cigarette production is to be discontinued temporarily in order to collect in two containers, for the same time interval, the tobacco not yet wrapped in the paper as outflowing from the rod formation, and the trimmed tobacco, respectively. Thereafter, by weighing these two collected amounts and by calculating the ratio between the weight of the trimmed tobacco and the total weight of the tobacco coming from the trimming and rod-formation steps, the percentage of recirculated tobacco will be obtained.
The optimum value of this percentage is a typical characteristic in cigarette manufacturing, and it must be set in a cigarette making machine at the beginning of the manufacturing process. Practically, however, during the manufacturing process, deviations or drifts occur between said pre-set optimum value and the actual value of the percentage of recirculated tobacco. These deviations, in the present status of the art, are determined and corrected by calculating the values of the percentage at pre-established intervals, and by regulating as necessary the total flowrate of the cut tobacco fed by the distributor. Of course, these calculations cannot be made too often, as they entail the shutdown of the operation.
Summarizing, the present regulation of the percentage of recirculated tobacco is performed in an empirical operation to be repeated from time to time, with obvious inconveniences.
The invention aims to thoroughly eliminate these drawbacks, and for this purpose it provides a control device for automatically regulating the percentage of cut tobacco being recirculated as trimmed excess tobacco, said device being adapted to match, substantially continuously, the actual value of said percentage with a pre-set optimum value of said percentage. This regulation is effected without interrupting the manufacturing of the cigarette rod, continuously and during successive time intervals which are equal to each other and adjustable, so as to automatically regulate accordingly the total flowrate of cut tobacco fed by the distributor.